Nutrient losses in surface irrigation runoff

Abstract

Runoff from surface-irrigated fields is typically managed to improve infiltration uniformity by reducing differences in infiltration opportunity times between the upper and lower ends of fields. Runoff water not used on other fields within an irrigation tract is discharged to streams or rivers, along with sediment and nutrients. Return flow nutrient and sediment concentrations may be greater than in the diverted water, but the total sediment and nutrient mass returned may be less if most of the diverted water infiltrates within the irrigation tract. Controlling erosion reduces total phosphorus loss, because total phosphorus concentration relates directly to sediment concentration. On-farm management practices, such as polyacrylamide (PAM) application and conservation tillage, reduce erosion from fields, while sediment ponds in the field or on return-flow streams trap suspended sediment that is not controlled by on-farm practices. Surface irrigation return-flow water quality can be improved with an organized effort using a combination of practices.